1. Field of the Invention
This invention relates to a device for sorting sheets discharged consecutively from an image forming device such as a copying machine to collate the sheets into sets in paging order, and more particularly to an automatic sheet sorting device having sheet pressure members for preventing interference of the sheets discharged from the image forming device with the sheets introduced previously into multi-stage sorting trays.
2. Description of the Prior Art
There has been used a sheet sorting device (sorter) for automatically distributing copy sheets or printed sheets consecutively discharged from an image forming device such as a copying machine, printing machine and printer into sorting trays aligned in multiple stages while collating the sheets in paging order. That is, a plurality of copy sheets or printed sheets reproduced from one original are fed one by one to the respective sorting trays in order, thus forming sets of copy sheets put in order of page. This sheet sorting device is applied as a finishing system or bookbinding system for the image forming device.
Although the number of copies can be increased with increasing the sorting trays in number, the increase of the sorting trays adds to the size of the sorting device. There are not infrequently found sorting devices having several tens of sorting trays aligned vertically, in which the interval between the adjoining sorting trays is conventionally reduced to diminish the size of the device.
However, the sheet discharged from the image forming device is not always flat, and particularly, it discharged from the copying machine, laser printer or the like, in which images formed with toner are fixed with heat, is by and large curled or deformed, consequently entailing a disadvantage such that the sheets are not neatly ensconced in the sorting tray and impedes successful admission of the following sheet into the sorting tray.
In a sorting device described in U.S. Pat. No. 4,576,371, a copy sheet is positively curved with its middle portion rising so as not to interrupt the next copy sheet, by using a pair of feed rollers different in diameter which are disposed confronting the entrance of a sorting tray. However, since the sheet is curved by the feed rollers before entering the sorting tray, it is apt to be caught by the entrance of the sorting tray or interrupted by the rising middle portion of the sheet earlier introduced into the sorting tray. Consequently, the interval between the vertically adjoining sorting tray cannot be narrowed, resulting in a large overall size.
As another measure, the sorting tray may be provided with electrical sheet pressure members which are operated by electric actuators for pressing down the sheets stacked on the sorting tray, and resultingly, it is complicated in structure and calls for an advanced controlling system which renders the handling of the device difficult.
Thus, there has been a need for a sheet sorting system capable of rationally and reliably distributing and sorting the sheets into the respective sorting trays at high speed without entailing problem such as increase in device size.